Storage subsystems, such as magnetic tape libraries, are widely used for storing information in digital form. These tape subsystems may include a storage subsystem controller for controlling one or more tape drives contained within the storage subsystem and for controlling other components of the storage subsystem, such as the tape picker, which is used to select and load tape cartridges into the tape drives. The storage subsystem may be coupled to a host system which transmits I/O requests to the storage subsystem via a host/storage connection.
Each tape drive reads and writes data to the primary storage medium, which can be, for example, a magnetic tape medium contained within a removable storage media device, such as, e.g., a removable magnetic tape cartridge or cassette. The magnetic tape medium typically comprises a thin film of magnetic material which stores the data. The tape medium may be moved by the tape drive between a pair of spaced apart reels and past a data transducer to record or read back information. In one type of tape drive system, one of the reels is part of the tape drive while the other reel is part of the removable tape cartridge. For this type of tape drive system, the reel which is a part of the tape drive is commonly referred to as a take-up reel, while the reel which is a part of the tape cartridge is commonly referred to as a cartridge reel. In another type of tape drive system, both reels are contained in a removable tape cassette.
Various methods have been used for loading a tape cartridge into a tape drive. In some automated loading systems, the tape cartridge is inserted into the tape drive by, for example, a robotic picker mechanism. The picker arm is typically configured to apply a force to the back of the tape cartridge to fully insert the tape cartridge into the tape drive. Upon insertion of the tape cartridge into the tape drive, a reel driver gear having a set of teeth matching a set of gear teeth provided on the bottom of the cartridge reel rises to couple with cartridge reel in the tape cartridge. A take-up reel of the tape drive is coupled to the cartridge leader on the magnetic tape and draws the magnetic tape out of the tape drive, past the data transducer, and onto the take-up reel. In this type of manual loading system, the tape cartridge travels in a single plane during the loading process. The picker mechanism provides the insertion force in a horizontal direction to drive the front of the cartridge to the location where the take-up leader coupling is to occur. Once the tape cartridge is firmly seated in the tape drive, the reel driver in the tape drive rises in the vertical direction (orthogonal to the horizontal insertion direction) to couple with the cartridge reel.
In other systems, sometimes referred to as “soft load” systems, the tape cartridge is placed in an initial loading location by the picker mechanism or by a human operator. The tape drive then assumes control of the tape cartridge and repositions the tape cartridge into the fully loaded location. This positioning typically involves translating the tape cartridge first in the horizontal direction and then in the vertical direction until a stationary reel driver in the tape drive couples with the cartridge reel. Soft, load systems can enable the tape drive to more accurately locate the tape cartridge in the final loaded positioning, free from the effects of a manual human load or library robotics variations.
Existing tape drive architectures may use sensors of different types to detect different conditions existing in the drive. These sensors, however, operate according to a one-to-one relationship between the condition a sensor is designed to detect and the sensor itself. For instance, a first sensor may be used to detect when a cartridge is present in a drive, while a second sensor may be used to determine the type of cartridge that is present, while a third sensor may be used to determine if the cartridge is in a position in the drive such that a load operation may be initiated. Unfortunately, as the number of sensors utilized in a given drive increases, the cost and complexity of the drive typically increases as well. Accordingly, it may be desirable to provide a tape drive architecture with sufficient ability to detect relevant conditions during operation while decreasing the overall cost and complexity of the drive.